Key Points
Question
Is systemic oxidative stress-induced damage to RNA and DNA increased in community-dwelling individuals with psychiatric illness and associated with all-cause mortality?
Findings
In this cohort study, oxidative stress-induced damage to RNA was increased in individuals with psychiatric illness and showed a dose-response association with mortality.
Meaning
The findings suggest that RNA damage from oxidation may be a mechanism in the accelerated aging observed in psychiatric illness and could have utility as a marker of mortality risk in these common disorders.
This cohort study evaluates the association between oxidative stress on nucleic acids and all-cause mortality in individuals with and without psychiatric illness.
Abstract
Importance
All-cause mortality and the risk for age-related medical disease is increased in individuals with psychiatric illness, but the underlying biological mechanisms are not known. Oxidative stress on nucleic acids (DNA and RNA; NA-OXS) is a molecular driver of aging and a potential pathophysiological mechanism in a range of age-related disorders.
Objective
To study the levels of markers of NA-OXS in a large cohort of community-dwelling individuals with and without psychiatric illness and to evaluate their association with prospective all-cause mortality.
Design, Setting, and Participants
This cohort study used a combined cohort of participants from 2 population-based health studies: the Danish General Suburban Population Study (January 2010 to October 2013) and nondiabetic control participants from the Vejle Diabetes Biobank study (March 2007 to May 2010). Individual history of psychiatric illness was characterized using register data on psychiatric diagnoses and use of psychotropic drugs before baseline examination. Urinary markers of systemic RNA (8-oxo-7,8-dihydroguanosine [8-oxoGuo]) and DNA (8-oxo-7,8-dihydro-2’-deoxyguanosine [8-oxodG]) damage from oxidation were measured by ultraperformance liquid chromatography–tandem mass spectrometry. Cox proportional hazard regression models were applied for survival analyses, using register-based all-cause mortality updated to May 2023. The follow-up time was up to 16.0 years.
Exposures
History of psychiatric illness.
Main Outcomes and Measures
Mortality risk according to psychiatric illness status and 8-oxoGuo or 8-oxodG excretion level.
Results
A total of 7728 individuals were included (3983 [51.5%] female; mean [SD] age, 58.6 [11.9] years), 3095 of whom (40.0%) had a history of psychiatric illness. Mean (SD) baseline 8-oxoGuo was statistically significantly higher in individuals with psychiatric illness than in those without (2.4 [1.2] nmol/mmol vs 2.2 [0.9] nmol/mmol; P < .001), whereas 8-oxodG was not. All-cause mortality was higher in the psychiatric illness group vs the no psychiatric illness group (hazard ratio [HR], 1.44; 95% CI, 1.27-1.64; P < .001) and increased sequentially with each increasing tertile of 8-oxoGuo excretion in both groups to an almost doubled risk in the psychiatric illness/high 8-oxoGuo group compared to the no psychiatric illness/low 8-oxoGuo reference group (HR, 1.99; 95% CI, 1.58-2.52; P < .001). These results persisted after adjustment for a range of potential confounders and in a sensitivity analysis stratified for sex.
Conclusions and Relevance
This study establishes systemic oxidative stress-induced damage to RNA as a potential mechanism in the accelerated aging observed in psychiatric disorders and urinary 8-oxoGuo as a potentially useful marker of mortality risk in individuals with psychiatric illness.
Introduction
Oxidative stress occurs when levels of reactive oxygen species, which are mainly formed during mitochondrial respiration, exceed the antioxidant potential of a biological system and cause oxidative damage to proteins, lipids, and nucleic acids, among others.1 We recently showed that across the psychiatric diagnostic spectrum, oxidative stress–induced damage to nucleic acids (DNA and RNA; NA-OXS) is increased in individuals with psychiatric illness compared to control individuals.2 Due to the evidence that NA-OXS is causally involved in aging and age-associated disorders, such as type 2 diabetes, dementia, cardiovascular disorders, and cancer,1 we speculated that a generally increased load of NA-OXS in psychiatric illness could be a potential mechanism underlying accelerated aging in these disorders.3,4 A logical extension of that notion would be that the levels of NA-OXS would be associated with mortality risk in patients with psychiatric illness. To test this hypothesis, we performed a large-scale molecular-epidemiological study of community-dwelling individuals with and without a history of psychiatric illness. In a recent study,5 we found that a marker of systemic oxidative stress on RNA, but not its DNA counterpart, was associated with mortality in the general population and patients with type 2 diabetes. Hence, we hypothesized that oxidative stress on RNA would be associated with mortality in individuals with psychiatric illness.
Methods
We combined data from 2 independent community studies: nondiabetic control participants from the Vejle Diabetes Biobank (January 2010 to October 2013; total = 4255; individuals with urine sample = 4079),6 and participants in the Danish General Suburban Population Study (March 2007 to May 2010; total = 21 203, individuals with urine sample = 3649),7 yielding a total population of 7728. The baseline variables (including hemoglobin A1c) of the subcohorts did not differ substantially, except for higher body mass index in the Danish General Suburban Population Study (eTable 1 in Supplement 1). We have previously studied the association between oxidative stress and mortality in type 2 diabetes and in the general population using these cohorts.5 Here, we used data from national Danish registries on hospital International Classification of Disease version 10 diagnoses of psychiatric illness from 19948 and redeemed prescriptions of psychotropic drugs from 19959 to dichotomize the cohort into individuals with and without psychiatric illness before the date of examination. Individuals were classified as having a history of psychiatric illness if they had either redeemed at least 1 prescription of a psychotropic drug or received a diagnosis of a psychiatric disorder in the period between the database inception to the date of their examination. All other individuals were classified as not having psychiatric illness. Finally, the date of death from all causes was retrieved from the Danish National Causes of Death Register,10 updated to May 2023. Causes of death were not available in this update. The urinary RNA and DNA oxidation markers 8-oxo-7,8-dihydroguanosine (8-oxoGuo) and 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodG), respectively, were measured using a validated and precise ultraperformance liquid chromatography-tandem mass spectrometry.11,12
The predefined primary outcome in the survival analysis was death from all causes. We constructed tertiles of 8-oxoGuo and 8-oxodG from the full data set to allow for comparisons of mortality risk in the no psychiatric illness vs psychiatric illness groups at the same absolute 8-oxoGuo and 8-oxodG excretion levels. Cox proportional hazards regression analysis with age as the underlying time scale was performed in which individuals were followed up from age at recruitment until age at end of follow-up or death. Results adjusted for age, sex, and study site are presented if not otherwise stated (see eMethods in Supplement 1 for details).
VDB was approved by the Regional Scientific Ethical Committees for Southern Denmark, GESUS was approved by the Regional Ethics Committee of Zealand, Denmark, and both were reported to the data authority in the Capital Region of Denmark in accordance with Danish and European legislation. All participants gave written informed consent before inclusion. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline was followed.
Results
Of 7728 individuals included, 3983 (51.5%) were female and 3745 (48.5%) were male, and the mean (SD) age was 58.6 (11.9) years. Sociodemographic and biochemical data for the 2 groups are presented in Table 1, and the diagnostic and pharmacological profile of the population with psychiatric illness is presented in eTable 2 in Supplement 1. At examination, 3095 of 7728 participants (40.0%) had a history of psychiatric illness. Mean (SD) baseline 8-oxoGuo was statistically significantly higher in the psychiatric illness group than in the no psychiatric illness group (2.4 [1.2] nmol/mmol vs 2.2 [0.9] nmol/mmol; P < .001), whereas mean (SD) 8-oxodG was not (1.8 [0.9] nmol/mmol vs 1.7 [0.8] nmol/mmol; P = .07). The follow-up time was up to 16.0 years, during which 1015 individuals died; 502 of 4633 (10.8%) in the no psychiatric illness group and 513 of 3095 (16.6%) in the psychiatric illness group (HR, 1.44; 95% CI, 1.27-1.64; P < .001). Mortality was higher in individuals with a hospital diagnosis of psychiatric illness vs individuals with psychotropic use only (HR, 1.67, 95% CI, 1.32-2.11; P < .001).
Table 1. Baseline Clinical, Sociodemographic, and Biochemical Variables of the Study Cohorta.
| Variable | Mean (SD) | P value | |
|---|---|---|---|
| N-PI (n = 4633) | PI (n = 3095) | ||
| 8-oxoGuo, nmol/mmol creatinine | 2.2 (0.9) | 2.4 (1.2) | <.001 |
| 8-oxodG, nmol/mmol creatinine | 1.7 (0.8) | 1.8 (0.9) | .07 |
| Study site, No. (%) | |||
| VDB | 2537 (54.8) | 1542 (49.8) | <.001 |
| GESUS | 2096 (45.2) | 1553 (50.2) | |
| Age, y | 57.4 (12.0) | 60.2 (11.4) | <.001 |
| Sex, No. (%) | |||
| Male | 2504 (54.0) | 1241 (40.1) | <.001 |
| Female | 2129 (46.0) | 1854 (59.9) | |
| Current smoking | |||
| No | 3864 (83.8) | 2358 (76.9) | <.001 |
| Yes | 749 (16.2) | 709 (23.1) | |
| Annual income, 1000 DKKb | 403.4 (235.8) | 368.2 (227.6) | <.001 |
| Body mass indexc | 24.3 (4.5) | 24.7 (5) | .001 |
| Systolic blood pressure, mm Hg | 142.1 (21.3) | 141.3 (20.9) | .08 |
| Diastolic blood pressure, mm Hg | 85.9 (11.3) | 85.5 (11.2) | .08 |
| Hemoglobin A1c, mmol/mol; % of total hemoglobin | 36.9 (4.8); 5.5 (0.4) | 37.7 (5.1); 5.6 (0.5) | <.001 |
| C-reactive protein, median (IQR), mg/L | 1.2 (0.6-2.7) | 1.3 (0.7-3.1) | <.001 |
| eGFR | 82.8 (16.2) | 81.6 (17) | .002 |
Abbreviations: 8-oxoGuo, urinary 8-oxo-7,8-dihydroguanosine excretion; 8-oxodG, urinary 8-oxo-7,8-dihydro-2’-deoxyguanosine excretion; eGFR, estimated glomerular filtration rate; GESUS, the Danish General Suburban Population Study; N-PI, participants without a register-based history of psychiatric illness; PI, participants with a register-based history of psychiatric illness; VDB, Vejle Diabetes Biobank.
Data were analyzed with t tests, Mann-Whitney U tests, or χ2 tests, as appropriate.
To convert to US $, based on rates at time of publication, divide by 6.9.
Calculated as weight in kilograms divided by height in meters squared.
All-cause mortality increased sequentially with each increasing tertile of 8-oxoGuo excretion in both the psychiatric illness group and the no psychiatric illness group, as reflected by a nonsignificant test for interaction (χ22 = 0.72; P = .70) (Figure, A). Hence, in a model without interaction between 8-oxoGuo level and psychiatric status, the increase in mortality risk vs 8-oxoGuo tertile was: HR, 1.10; 95% CI, 0.92-1.31; P = .32 (medium vs low) and HR, 1.39; 95% CI, 1.17-1.66; P < .001 (high vs low); adjustment for the marker level did not change the mortality estimate of psychiatric illness vs no psychiatric illness (HR, 1.44 95% CI, 1.27-1.63; P < .001).
Figure. All-Cause Mortality vs Psychiatric Illness and Oxidative Stress-Induced Damage to Nucleic Acids.
Data are presented as forest plots of the risk of all-cause mortality in individuals with a register-based history of psychiatric illness (PI) and without a register-based history of PI (N-PI) as a function of systemic levels of oxidative stress-induced damage to RNA (A) and DNA (B). The analytical groups are derived from PI status and tertiles of the marker level excretion (low, medium, and high), determined from the full data set. Data were analyzed by Cox proportional hazard regression models without an interaction term and adjusted for age (by using it as the underlying time scale), sex, and study site (model 1), presented as hazard ratios (HRs) with 95% CIs.
An overlap in mortality risk was observed, where mortality was similar in the no psychiatric illness/high 8-oxoGuo group vs the psychiatric illness/low 8-oxoGuo group and increased further to an almost doubled risk in the psychiatric illness/high 8-oxoGuo group compared to the no psychiatric illness/low 8-oxoGuo reference group (HR, 1.99; 95% CI, 1.58-2.52; P < .001) (Figure, A). For 8-oxodG, a nonlinear association with weaker associations between the marker level and mortality risk emerged, both before and after the full adjustment (Figure, B and Table 2).
Table 2. Cox Proportional Hazards Regression Analyses of Mortality Risk as a Function of Systemic Levels of Oxidative Stress (N = 7728)a.
| Group | No. | Model 1b | Model 2c | ||
|---|---|---|---|---|---|
| HR (95% CI) | P value | HR (95% CI) | P value | ||
| RNA (8-oxoGuo) | |||||
| N-PI low | 1696 | 1 [Reference] | NA | 1 [Reference] | |
| N-PI medium | 1572 | 1.08 (0.85-1.38) | .52 | 0.96 (0.75-1.23) | .76 |
| N-PI high | 1365 | 1.31 (1.04-1.66) | .02 | 1.21 (0.95-1.54) | .11 |
| PI low | 880 | 1.34 (1.01-1.77) | .04 | 1.21 (0.91-1.62) | .18 |
| PI medium | 1004 | 1.50 (1.17-1.92) | .001 | 1.31 (1.02-1.69) | .03 |
| PI high | 1211 | 1.99 (1.58-2.52) | <.001 | 1.72 (1.35-2.18) | <.001 |
| DNA (8-oxodG) | |||||
| N-PI low | 1549 | 1 [Reference] | NA | 1 [Reference] | |
| N-PI medium | 1561 | 0.76 (0.61-0.95) | .02 | 0.81 (0.65-1.02) | .08 |
| N-PI high | 1523 | 1.00 (0.81-1.23) | .98 | 1.04 (0.83-1.30) | .73 |
| PI low | 1027 | 1.44 (1.16-1.79) | <.001 | 1.43 (1.14-1.79) | .002 |
| PI medium | 1015 | 1.12 (0.90-1.41) | .31 | 1.11 (0.88-1.40) | .37 |
| PI high | 1053 | 1.42 (1.14-1.76) | .002 | 1.35 (1.08-1.69) | .01 |
Abbreviations: 8-oxodG, urinary 8-oxo-7,8-dihydro-2’-deoxyguanosine excretion; 8-oxoGuo, urinary 8-oxo-7,8-dihydroguanosine excretion; HR, hazard ratio; NA, not applicable; PI, participants with a register-based history of psychiatric illness; N-PI, participants without a register-based history of psychiatric illness.
The groups are derived from the register-based history of psychiatric illness status (N-PI and PI) and tertiles of the marker-level excretion (low, medium, and high), determined from the full data set. Because the absolute levels of the RNA and DNA oxidation markers differed in the PI vs N-PI groups, the distribution of individuals within each tertile also differs.
Model 1 is adjusted for age (by using it as the underlying time scale), sex, and study site.
Model 2 is further adjusted for smoking status, individual income, body mass index, hemoglobin A1c, log-transformed plasma C-reactive protein concentration, and calculated glomerular filtration rate.
These results were preserved, although slightly attenuated, after the full adjustment in model 2 (Table 2). Finally, in a sensitivity analysis stratified for sex, the findings were not materially altered (eTable 3 in Supplement 1).
Discussion
In this cohort study, we confirmed our recent finding2 that NA-OXS is increased in psychiatric illness; however, in this population of community-dwelling individuals with a minor psychiatric disease burden (based on the distribution of diagnoses and psychotropics used (eTable 2 in Supplement 1), we found this to be restricted to OXS on RNA. Furthermore, we demonstrated the biological significance of this phenomenon by showing that the RNA marker was associated with all-cause mortality, with higher mortality risk in individuals with psychiatric illness at the same absolute marker level and after adjustment for potential confounders. The association between 8-oxoGuo level and mortality was the same in the psychiatric illness group vs the no psychiatric illness group, pointing to a general aging phenomenon not specific to patients with psychiatric illness.
Psychiatric illness is associated with a range of biological stressors that may converge on increased oxidative stress, such as smoking, inflammation, and chronic neurohormonal stress.2 The downstream outcomes of messenger RNA oxidation include misfolding and dysfunction of proteins, whereas the oxidation of regulatory RNA species may influence cellular signaling pathways and metabolism. These phenomena may promote aging at the cellular level across organ systems.13
Strengths and Limitations
The limitations of the study are its observational nature, which precludes any conclusions on causality, and that causes of death were not available. The strengths include the large sample size from the general community and our ability to define psychiatric illness and mortality from objective register-based data spanning decades before and after participant inclusion.
Conclusions
In conclusion, the findings of this study suggest systemic oxidative stress-induced damage to RNA as a potential mechanism in the accelerated aging observed in psychiatric disorders, and urinary 8-oxoGuo as a potentially useful marker of mortality risk in individuals with psychiatric illness.
eMethods
eTable 1. Comparison of baseline clinical, sociodemographic and biochemical variables between the VDB and GESUS cohorts
eTable 2. Characterization of the psychiatric morbidity profile in the population of individuals from the full study cohort with a history of psychiatric illness
eTable 3. Cox proportional hazards regression analyses of mortality risk as a function of systemic levels of oxidative stress-induced damage
eReferences
Data sharing statement
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Associated Data
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Supplementary Materials
eMethods
eTable 1. Comparison of baseline clinical, sociodemographic and biochemical variables between the VDB and GESUS cohorts
eTable 2. Characterization of the psychiatric morbidity profile in the population of individuals from the full study cohort with a history of psychiatric illness
eTable 3. Cox proportional hazards regression analyses of mortality risk as a function of systemic levels of oxidative stress-induced damage
eReferences
Data sharing statement
